Integrated system for vaporizing cryogenic liquids

ABSTRACT

An integrated system for vaporizing cryogenic liquids including a fuel burner for generating hot combustion gases. The gases are directed into a mixing chamber and contacted with a spray of water for producing a heat transfer gas-steam mixture. The mixture is allowed to indirectly heat the cryogenic liquid and condensate formed is recycled for mixing. The firing rate of the burner is controlled in response to the temperature of the gassteam mixture exhaust.

Nov. 6, 1973 United States Patent [191 Linhardt et al.

[54] INTEGRATED SYSTEM FOR VAPORIZING 3,364,982 1/1968 Jaffe 165/60CRYOGENIC LIQUIDS [75] lnventors: Hans A. Linhardt; James A. Kirk, P iar Examiner-Charles Sukalo both of Costa Mesa; Raymond E-Att0rney-Mathews et a1. Lancaster, San Pedro, all of Calif.

[73] Assignee: Airco, Inc., New York, NY.

ABSTRACT [22] Filed:

Dec. 22, 1971 A L N 210,713 An integrated system for vaporizingcryogenic liquids including a fuel burner for generating hot combustiongases. The gases are directed into a mixing chamber 165/1 165/39 andcontacted with a spray of water for producing a 1/00 heat transfergas'steam mixture. The mixture is allowed 62/52; 55/60, to indirectlyheat the cryogenic liquid and condensate [52] U.S. [51] Int. [58] Fieldof Search 165/39 40 formed is recycled for mixing. The firing rate ofthe burner is controlled in response-to the temperature of References(mad the gas-steam mixture exhaust. UNITED STATES PATENTS 3,246,634Stevens................................... 62/52 22 Claims, 7 DrawingFigures PATENTEU NOV 6 I975 INVENTORS.

H D LINHARDT SHEET 16F 4 J.A. KIRK R. E. LANCASTER 8) 1 3 ATTOR 5yPATENTEU NOV 6 I973 SHEET 2 BF 4 f HOT GAS-STEAM M/X TURE INVENTORS. H.D. LINHARDT R. E. LANCASTER 8) F3 M FIG. 2

PATENTEDRUV 6 I975 3.770.048 SHEET 36F 4 FIGA L P u F L C J. A. KIRK R.E. LANCA ATT INVENTORS H D LINHARDT STER PATENTEDmv 6 191a SHEET M 0F 4.QEQ

/NVE N TORS.

H. D. LI'NHARDT J. A. KIRK R. E. LANCASTER ATTORNEY INTEGRATED SYSTEMFOR VAPORIZING CRYOGENIC LIQUIDS BACKGROUND OF INVENTION The prior artdiscloses heat transfer systems of the type wherein a continuous flow ofhot gases heats a fluid that is circulated through heat conducting tubesdisposed in the path of the hot gases. Systems of this kind have beenused in aircraft, for example, wherein hot exhaust gases from a jetengine are used for heating air that is circulated through a heatexchanger. The heated air in turn is used for space heating, air-foildeicing and the like.

It has also been proposed to vaporize cryogenic liquids in asubmersion-type heat exchanger wherein one or more fuel burners directhot exhaust gases at superatmospheric pressure through ducts into a bodyof water that in turn surrounds heat transfer passages for thecirculating cryogenic liquid. In this two-stage arrangement, the wateris heated by direct bubbling contact with the hot exhaust gases, and theheated water vaporizes the cryogenic liquid within the heat transferpassages. The two-stage systems are generally installed in large pouredconcrete tanks which contain the water bath. Such systems are expensiveand complicated in assembly and cannot be skid-mounted and easilytransported. These systems do, however, provide for moderating thetemperature gradient between the hot gases and the cold liquid.

Where hydrocarbon cryogenic liquids, such as LNG (liquified natural gas)or methane, etc. are to be vapor ized for piping into commercial storageordistribution lines, this temperature moderating effect referred toabove, is not only desirable but is especially important for safeoperation. For such liquids, application of excessive heat to the heattransfer surfaces can be hazardous and result in explosions, fires, etc.It is also desirable that the gaseous heat transfer medium have a verylow oxygen content for safe operation, as well as for minimizing tubedeterioration, etc.

A single-stage heat transfer system utilizing hot com bustion gases incombination with water injection for producing a heat transfer mediumconsisting of a hot mixture of gas and steam for vaporizing cryogenicliquids and the like, is described and claimed in a copendingapplication Ser. No. 880,041, for Hot Gas Heat Exchanger," filed Nov.26, 1969 by H. D. Linhardt and assigned to the same assignee as thepresent invention. The present invention constitutes an improvement onthe single-stage system described therein.

As used herein, the term cryogenic liquid is intended to mean a liquid,ordinarily a gas at ambient temperature, that requires a temperaturematerially below the freezing point of water for keeping it in aliquefied state. Typical of such cryogenic liquids are nitrogen, oxygen,natural gas, methane, etc.

SUMMARY OF THE INVENTION In accordance with the invention an integratedheat transfer plant for vaporizing a cryogenic liquid comprises in apreferred arrangement, a heavy duty industrial fuel type burner equippedwith an intake air blower or compressor, a combustion chamber for com--pleting the combustion process and having water injection for steamgeneration, a heat transfer and'vaporizing chamber receiving thegas-steam mixture from the combustion chamber and containing heatconducting tubes for circulating the cryogenic liquid, and a condensatesump with water recovery pump means for recirculating injection waterand cooling water, together with controls for achieving efficient anduniformly high rate of vaporization of the cryogenic liquid to a productgas. In one form of the invention, the component units of the plant arecompactly mounted on a common base for making up an integrated assemblythat can readily be installed.

Practice of the invention comprises essentially feeding compressed airfrom the blower to the fuel burner for producing large volumes of hotcombustion gases; these gases in turn flow into a water cooledcombustion chamber for completion of combustion and then cooling byspray water. Water is directed to fogging spray nozzles to create a mistwhich is thoroughly mixed with the combustion gases to make up agas-steam mixture. This heat transfer medium is directed into andthrough the heat transfer and vaporizing chamber containing multipleheat transfer coils or tube bundles arranged in a stack, through whichflows the cryogenic liquid to be vaporized and superheated. Capacitycontrol for efficient and safe operation is maintained by mutuallyrelated modulating and other controls. For example, efficient generationof heat for the vaporization process is achieved by adjusting burnerfuel-air feed according to variation in the stack end temperature of thevaporizer; e.g., exhaust gas temperature from a selected referencevalue; the fuel-air ratio may be subject to control by varying thevolume of blower air according to sensed burner oxygen for ensuring nearstoichiometric condition. Accordingly, significant oxygen content in theheat transfer mixture is avoided. The temperature of the product gasleaving the vaporizer is also sensed and controlled to avoid widefluctuations.

A principal object of the invention therefore is an improved heattransfer system for vaporizing cryogenic liquid by a gas-steam mixture,that provides for full capacity control at a high rate of heat transfertogether with safe operation at high thermal efficiency.

A related object is a readily installed unit-type vaporizer plant of thecharacter above, including components making up an integrated systemthat is economical as regards both initial cost and maintenance, andthat has a practical minimum of controls.

Other objects, features and advantages will appear from the followingdescription with reference to the accompanying drawings' BRIEFDESCRIPTION OF DRAWINGS FIG. 1 is a lengthwise view in elevation, brokenat several sections for overall illustration, of cryogenic liquidvaporizing apparatus embodying the present invention;

FIG. 2 is an end view of FIG. 1 in elevation showing vaporizer stackunit connections;

FIG. 3 is an enlarged interior view of one of the heat transfer tubeunits making up the vaporizer stack, taken as viewed in FIG. 1;

FIGS. 4 and 5 are similar-enlarged interior views of the tube unit ofFIG. 3, taken as viewed in FIG. 2, and from the top respectively; 1

FIG. 6 is a schematic diagram of the stacked tube units connected asgenerally indicated in FIG. 2; and

FIG. 7 is aschematic system diagram of a preferred form of theinvention.

DESCRIPTION OF PREFERRED EMBODIMENT The cryogenic liquid vaporizingapparatus of FIGS. 1 and 2 comprises essentially a heavy duty fuelburner 10, for directing flames and the products of combustion into along horizontal tunnel-like combustion chamber 14 for obtaining completecombustion of the burner gases, a spray chamber 16 constituting acontinuation of the tunnel into which water is injected for generating agas-steam heat transfer mixture and finally a vaporizing tower or stack20 constituting a heat exchanger through which the gas-steam mixturefrom the chamber 16 is directed for vaporizing a cryogenic liquid suchas liquefied natural gas. A flow-guide elbow 19 interconnects the spraychamber and stack 20 for directing the gas-steam mixture into the stack.The combustion tunnel is water jacketed for cooling purposes and forrecovering heat therefrom.

The vaporizing stack 20 is made up of vertically aligned andinter-connected heat transfer tube units or sections 22, 24, 26 and 28,each unit comprising a tube bundle of multiple coils as diagrammaticallyrepresented in FIG. 6 for circulation of the liquid to be vaporized.

The main vaporizer plant as shown in FIGS. 1 and 2 is mounted on astructural steel base 21 that in practice may be positioned on aconcrete pad (not shown) for outdoor operation. Auxiliary equipment(fuel-air control, etc.) associated with the burner and blower 11 isgenerally indicated at 4, 5, 6, 23. Base saddles such as at 25 supportthe combustion tunnel l4 and permit free movement due to expansion andcontraction. Supports 29 serve to maintain the stack in position. Theforward end of the burner section 12 is bolted to a flange on the end ofthe chamber 14. A plate 27 supports the forward end of the burner on acarriage 13, which may be rolled away from the chamber 14. Thus byunbolting the flanged connection 27a, the burner may be rolled back forinspection, repair, etc.

The blower unit 11 includes a motor driven fan (not shown), an airintake 2, controlled by pivotally mounted vanes 3 which are in turnactuated by suitable linkage and gearing 4, 5. Connected to linkage 4 isa further linkage 6 which operates a valve 7 which controls the flow ofthe fuel (for example natural gas) to the burner 10. The fuel supply isconnected to pipe 8. An actuator 23 operates through a linkage 23a tosimultaneously vary the air supply and the fuel supply, thereby assuringproper stoichiometric mixing and substantially complete combustion ofthe fuel. The actuator is preferably operated automatically in responseto the temperature of the stack exhaust gases as will be describedhereinbelow.

The air blast generated in blower unit 11 passes through an expansionchamber 10a which serves to distribute the air blast uniformly through aplurality of burner nozzles mounted on annular manifold 12. The manifoldis fed with a fuel supply from intake line 8. The burner nozzlescomprise a plurality of tubes (one of which is shown) extending radiallyinwardly from the annular manifold. Each tube 12a has a plurality ofholes 12b drilled therein, along its length facing downstream wherebyfuel is distributed from each tube along its length. This arrangement offuel supply provides for substantially even distribution of fuel in theair supply and results in substantially complete combustion of the fuel.

Suitable safety shutoff valves are placed in the fuel line 8 forshutting down the fuel supply, such as when the fire eye indicates lossof flame, etc. These safety valve are conventionally required by localcodes and will not be described further.

The hot flames of combustion are directed from the area of the ring 12downstream into a cylindrical, water-cooled combustion chamber 14. Thechamber length is of a design such that under maximum desired firingrate conditions the combustion of the fuel will be sutstantially fullycompleted prior to the combustion products reaching the mixing chamber16 wherein the fogging nozzles are located. The chamber 14 comprises anouter steel cylinder wall and a concentric inner steel cylinder wall.

One or more helical baffles 153 are positioned between the concentriccylindrical walls to direct the cooling water in a helical pattern fromone end of the chamber 14 to the other. Water is introduced into thedownstream end of the cooling chamber by means of a pipe 154 connectedto a motor driven pump 17 located in sump 15. The cooling water flowsupstream in a helical pattern. The water passing through the annuluscools the chamber walls and prevents the buckling or deterioration ofthe walls. The water is heated and a portion of it may in fact beconverted into steam. The heated water and/or steam exhausts through areturn pipe 160A, or pipes if more than one helix is used, which directsthe exhaust to a point approximately one third up in the lower stackunit 22. The exhaust is sprayed into the lower stack unit wherein it iscooled against the tube bundle. The cooled liquid and any condensate maythen run down the tube bundle, through elbow 19 and return to the sump15 via pipe 150. The cooled water may then be recirculated to thechamber 14 by the sump pump 17. Thus the water and steam which has beenheated and generated in the cooling passages of chamber 14, is used towarm the cryogenic liquid passing through the tube bundle in unit 22. Inorder to further protect the interior wall of the inner cylinder ofchamber 14, the inner wall may be coated with a refractory material.

The water spray or fog is injected into a chamber 16 as jets fromperipherally spaced nozzles 80, FIG. 2, that are mounted in the chamberwall so as to direct the individual fogging jets on a downstream angle(about 45) towards the longitudinal axis of the chamber, FIGS. 1 and 7.The combined jet pattern thus defines a thick cone-like screen of waterspray across the chamber through which the combustion tunnel gases aredirected for cooling and steam generation. The jet nozzles (five in thepresent example) are supplied with water under pump pressure from thewater sump pump 17a and manifold 160, FIG. 1, to which the respectivejet feed pipes 161 are connected in parallel for spraying largequantities of water into the hot combustion gases. Due to the hightemperature of the combustion gases, a large part of the water fog isinstantly converted into steam; the resulting cooled mixture consistingof the burner gases, steam and water mist flow upwardly through theguidance elbow 19 containing guide vanes 84 into the lower end of thevaporizer stack 20, FIGS. 1 and 7. The vanes are fixed in the elbow forwall-to-wall extension with approximately equal spacing for defining theflow equalizing passages 86. As indicated by direction arrows, thegas-steam mixture is divided by the passages into multiple parallelstreams that are approximately equal in cross-section. The gassteammixture then passes upward through the stack of tube bundles to cool thefluid that is passing through the tube bundles. The operation andstructure of the tube bundles will be described more particularly below.

In order to reduce the amount of water escaping from the top of thestack, a spacer unit 28a is positioned over the top tube bundle. Thisunit defines a confined opening which permits a swirling or arecirculation of the exhaust gases. The top of the unit 28a is coveredby a roof to prevent entry of snow, etc. and enclosed by a screen 75which tends to prevent particle emissions. The spacer unit 28a alsocontains a plurality of troughs 750 which are arranged in a horizontalarray across the width of the unit 28a. Water vapor condenses on thetrough and the water formed therein is directed to a header connectingall the troughs which is in turn connected to a downcomer 76 which leadsback to the sump. Thus a portion of the water vapor which would haveexited the stack is returned to the sump for reuse.

Referring specifically to the stack arrangement of the cryogenic liquidtubes in FIG. 6, as related to the flow of the vaporizing heat transfermedium, the cyrogenic liquid (such as for example liquefied natural gas(LNG)) to be vaporized is admitted under pressure (such as from a pump)from a source such as conventional storage facilities, to a conduit orinlet main 46 from which the liquid divides at a junction 55 forrespective flow into the inlet pipe 44 of unit 22, and the inlet pipe 54of unit 24. The outlet pipe 42 of unit 22 is connected through anexterior inter-unit pipe 40 with the inlet pipe 38 of unit 28 sothat'the tube units 22 and 28 are in series flow. The outlet pipe 34 ofunit 28 is connected to the product gas outlet rnain 30.

Similarly, the tube units 26 and 24 are connected in series flow throughthe outlet pipe 52 of unit 24, interunit pipe 50, inlet pipe 48 of unit26, and outlet pipe 36 of unit 26 that in turn is connected at junction32 with the outlet pipe 30, to the exhaust main. In order to balance theheat transfer loading in the units 22 and 28, a small amount of liquidis by-passed around unit 22, by directing a quantity of LNG throughvalve 46a and line 46b into line 40. Thus, the LNG flow is through thevaporizer stack tubes in two separate branch paths connected inparallel, i.e., tube units 28 and 22 make up one branch and units 26 and24 the other. The parallel arrangement is ideally suited for lowpressure applications. For high pressure applications a seriesarrangement throughout the stack is more appropriate. In thisarrangement the flow of the LNG is cocurrent with the gas-steam mixtureas indicated, the two units 26 and 28 constitute the warm heat transferends respectively of the parallel branch paths. As these units receivethe heat transfer medium at the upper end of the stack, a sufficientlyhigh temperature gradient is maintained for final and completevaporization of LNG and adequate warming of the product gas within thetubes prior to venting into the outlet main 30. Flow through the tubesmaybe in counterflow to the hot gases; however, co-current flow has beenfound best for economy and good control.

a suitably prefabricated housing or shell 58 of box-like form open atits upper and lower ends. The housing has coupling flanges 59 and 60 atits open ends for joining with corresponding matching flanges ofadjoining stack units. The heat transfer tube bundle within the unitconsists of a number of tiers 62 of tube loops, each tier extendinggenerally throughout the height of the unit, the multiple tiers beingarranged in parallel, spaced order throughout the width of the unit,FIGS. 4 and 5. The series loops 66 of each tier constitute as bestshownin FIG. 3, an individual parallel branch path for LNG flow, therebyfurther dividing the flow into a large number of parallel paths within asingle tube unit. To

this end, the lower or inlet loop of each tier is connected at 57 to thesupply pipe 70. This pipe may lead from either the LNG inlet main 46, orfrom the outlet The structural unit arrangement of the tube assembly ofa preceding unit such as 42 for example. The outlet loop of the tier isconnected at 56, FIGS. 3 and 4, to a similarly arranged exterior pipe 68that may lead to either a series-connected unit or to the product gasoutlet main 30.

It will, therefore, be seen that by multiple division of flow within asingle unit as described above, the tube diameter in each tier can becorrespondingly reduced. Accordingly, there is an advantageous materialincrease in the ratio of heat transfer area to unit volume of LNG, thatin turn makes possible a material increase in rate of heat transfer forrapid vaporization.

For controlling the temperature of the product gas at the outlet main 30as hereinafter described in more detail, a valve 74 controlled bypassline 72, FIGS. 2 and 6 is connected across the inlet and outlet'mains 46and 30. The bypass valve 74 is controlled according to temperature ofthe product gas in the outlet main for bypassing some cold LNG into themain 30 to maintain a desired discharge temperature.

The spent gases reaching the top of the vaporizer stack, ordinarilycooled t'o'slightly above ambient temperature, are suitably vented toatmosphere as by a screen-enclosed deflector indicated at 75 afterpassing through the spacer unit and trough.

The system schematic of FIG. 7 shows control means for achievingstabilized full capacity flow and optimum performance of the vaporizersystem throughout a wide range of product gas demand. A primary fuel-airratio control is jointly applied to the burner fuel and blower airinputs at the unit 10-12 as hereinafter described. The single, heavyduty burner is capable of producing large volumes of hot combustiongases under dependable and efficient combustion conditions. In this type'burner, the combustion head provides for a high degree of flameretention under very wide operating load ratios. A conventional ignitionsystem having spark plugs and pilot light may be used wherein the pilotlight is shut off by automatic flame detectors after a set startingperiod. The details of the complete burner starting system, etc. neednot be described herein for an adequate understanding of the invention.

Assuming initially, that the burner-blower unit 10-12 is operating at anormally high rate of combustion, the operation generally of the'vaporizer plant is as follows. The burner combustion gases aredischarged at high velocity through the combustion tunnel 14. The gasesduring passage through the tunnel are in turbulent flow, therebyenhancing the final combining of remaining oxygen with unburned gases,including carbon monoxide (CO), for the stoichiometric condition set bythe burner control. Near the end of the tunnel, where combustion iscompleted and the gas temperature approaches 3,000 F, water is injectedinto the gases as they enter the spray chamber 16 for cooling down to atemperature within the range of about l20-350 F and preferably aboutl50-l90 F, suitable for stack vaporization of the cryogenic liquid, suchas natural gas. During this temperature drop, large quantities of steamare generated.

In the schematic of FIG. 7, the multiple branch heat transfer tube unitsof the stack 20, FIGS. 3 to 5, are represented for simplicity as asingle coil 90, with cold LNG from the inlet pipe 46 passing inco-current flow with respect to the gas-steam mixture for vaporizationand final flow as product gas from the outlet main 30. In thisarrangement, the temperature of the spent gases and vapors at the top(exhaust) of the stack 20 is an incicator of the rate of heat transferto the LNG tube bundles for vaporization, i.e., if the stack exhausttemperature is too low, heat transfer and vaporization rates are too lowand more burner heat must be added to the gas-steam mixture; conversely,if the stack temperature is too high, fuel is being wasted. I

For controlling the temperature of the vaporizing heat transfer mixture,a signal from a temperature indicator or gauge 92 that senses the stackexhaust temperature is transmitted to a temperature controller 100. Theoutput of the temperature controller 100 operates a positioner (whichmay for example be a pneumatic positioner) 23 which simultaneouslymodulates the fuel valve 7 and the vanes 3 of the blower.

Where the cryogenic liquid is to be vaporized is a combustible compoundsuch as methane, it is highly desirable that the heat transfer medium besubstantially free of oxygen, otherwise an explosion hazard can exist inthe event of a leak or accidental damage to the tube bundle. A lowoxygen heat transfer medium is also desirable for minimizing corrosion,etc. of the cryogen tubes, fittings, etc. For reducing oxygen in thegassteam mixture to a practical minimum, the burner fuelair ratio isadjusted by varying jointly and simultaneously the inputs of fuel andblower air according to an end-temperature condition at the vaporizerstack exhaust.

Although temperature regulation of the stack exhaust gases is also arough control of the product gas temperature in the outlet main 30, itdoes not except in a stabilized condition of constant output of thevaporizer, provide adequately close control. For example, where atransient condition exists, such as material change in product demand,there is a definite time lag between a change in flow rate of theincoming cold LNG at inlet main 46 and a responsive change intemperature of the stack gases. This time lag involves the varyingresponse time to fuel feed change, passage of the heat transfer mixturethrough the tunnel and stack, heat transfer lag, etc. in the stack andother factors.

For maintaining a stabilized condition wherein the outlet product gastemperature is to be held substantially at its norm, i.e., approximately60 F with a highlow tolerance of about 15 F, within the full range ofvaporizer operation from no flow to maximum flow, cold LNG is bled asrequired from the inlet main 46 through the bypass 72 directly into theoutlet main 30. The bypass valve 74 for such control is responsive to asignal from a thermocouple or temperature sensor connected in the outletmain 30 as indicated at 120. The

signal is fed to a temperature controller 126 for operating liquidbypass valve 74, according to variation of the sensed signal from thereference norm, i.e., 60 F. A pneumatic actuator may be used to operatevalve 74.

In practice, the LNG inlet pressure may be up to 1,200 psig; the inlettemperature is about 255 F. The pressure drop throughout the vaporizertubes is typically about 50 psig. Pressures in the inlet and outletmains are monitored respectively, by indicators or gauges 148 and 146.

Accordingly, the product gas temperature control as described above isindependent of and superimposed as a fine control on the main burnercontrol for insuring that the outlet-temperature of the product gas iskept within the accepted limits mentioned above. The main burner fuelcontrol, on the other hand, is comparatively coarse control based on atemperature signal from the thermocouple or sensor 92 at the stackexhaust.

The hot gas-steam mixture causes a high rate of heat transfer as thegases pass upward and into heat exchange contact with the cold cryogentubes. Any condensate formed will flow by gravity through the elbow 19and sump inlet 150 and collect in the sump 15. The sump condensate (plusmake-up water required due to loss of some moisture in the stack exhaustgases) constitutes the source of the spray water for steam generation.The sump pump 17a discharges condensate at substantially constantpressure through a pipe 162 with check valve 156, into the manifold 160.The make-up water supply is controlled in conventional manner by a floatoperator indicated at 172 for controlling the water inlet valve 174 soas to maintain the sump water level 176 substantially constant. Thetemperature of the sump water is also subject to control depending ondifferent operating conditions. For outdoor operation in cold weather,it may be necessary to supply additional heat to the condensate forpreventing freezing of the exterior lines 154, 162, etc. For thispurpose, suitable means such as an electric heater 180 is positionedwithin the condensate and is energized in response to a signal from atemperature sensor 182 for switching the heater on or off at 184.

Other auxiliary system controls may be initiated in conventional mannerfor starting, emergency venting, and plant shutdown, etc., in responsefor example to any significant irregularity or malfunction. Since thesecontrols are in general ordinary protective or backup arrangements,detailed descriptions thereof are not necessary for adequateunderstanding of the invention, other than to mention factors subject tomonitoring for possible shutdown and inspection, such as burner flamefailure, low (or high) fuel gas pressure, low blower pressure (sensornot shown), high temperature of mixture discharge from the spraychamber, and low air pressure for by-pass valve operation.

Performance specifications for a typical LNG vaporizing plant embodyingthe invention include the following:

BURNER AND GAS-STEAM HEAT TRANSFER MIXTURE Natural gas fuel: l2,000-l20,000 SCFH Mixture temperature at stack entrance: l50-l 90 F Heattransferred to LNG: lO-lOO 10 Btu/hr. Oxygen content, stack gases: Abouttwo percent PROCESS LNG inlet pressure: 300 psig LNG inlet temperature:225 F NG outlet pressure: 250 psig NG outlet temperature: 60: 15 F Flowrate of process: 15-125 X 10 SCFD The vaporizing plant also has a highdegree of flexibility such that the time required from first notice ofdemand (at start) to full flow of product gas is but minutes. Inaddition, the efficiency of the vaporizing system is normally high dueto the specific multia passage arrangement of the tube bundles inparallel flow to the gas-steam mixture for obtaining high rates of heattransfer. With this arrangement, best shown in FIG. 6, the initially hotgas-steam mixture contacting the lower tubes prevents excess freezing ofcondensate on the cold tube surfaces; the stack exhaust gases are cooledto about l l70 F and preferably about l30-l40 F.

Although the tube bundles are conveniently arranged in a vertical array,they may also be arranged in a-horizontal array or in any other arraywhichwould permit the exhaust gases to pass over them conveniently anwhich would permit water collection.

In brief, the disclosed embodiments of the invention make use of steamwhich is generated and recondensed within the system, as a materialcomponent of the heat transfer mixture. The gas-steam mixture as usedherein makes possible a high rate of vaporization of the cryogenicliquid, while protecting the tubes and liquid therein from excessivelyhigh temperatures, especially will probably also be 'used as a fuel,since it is readily available at low cost. If economic conditionsdictate, fuel oil or any other low cost fuel could be used.

Having set forth the invention in what is considered to be the bestembodiments thereof, it will be understood that changes may be made inthe system and apparatus as above set forth without departing from thespirit of the invention or exceeding the scope thereof as defined in thefollowing claims.

We claim:

1. A heat transfer system for vaporizing cryogenic liquid to a productgas comprising, a'fuel burner and air blower combination for producinglarge volumes of hot combustion gases, a combustion chamber into whichthe combustion gases are directed for completing combustion thereof,means for injecting water spray into the gases after substantiallycomplete combustion for vaporizing the water and producing a gas-steamheat transfer mixture, a heat exchanger through which the gas-steammixture from the combustion chamber is directed having passagesfor'circulation of the cryogenic liquid, the heat transfer mixture beingin direct heat exchange contact with the cryogenic passages forvaporizing the liquid to a product gas, means for sensing thetemperature of the heat transfer mixture leaving the exchanger, andmeans responsive to the temperature sensing means for controlling thefiring rate of the burner-blower combination to regulate the temperatureof the product gas leaving the exchanger passages.

2. A heat transfer system as set forth in claim 1 wherein the combustionchamber comprises an elongated cylinder of double-walled construction toform an annular cooling passage around the chamber, the outer of saidwalls having ports providing for the admission and exhaust of passagecooling water.

3. A heat transfer system as set forth in claim 2 further includinghelical baffle means between the walls of said cylinder to channel thecooling water flow in a helical pattern.

4. A heat transfer system as set forth in claim 1 wherein the heatexchanger comprises a plurality of tube bundles arranged in a verticalstacked array, said combustion chamber directing said heat transfermixture into the lower of said tube bundles whereby the mixture passesup through the vertical array.

5. A heat transfer system as set forth in claim 4 including means todirect the cryogenic fluid flow through said tube bundles in co-currentflow relationship with respect to the heat transfer mixture.

6. A heat transfer system as set forth in claim 4 including sump meansto collect liquid condensed on said tube bundles for reuse, and furthermeans to trap water leaving the heat exchanger and return the same tothe sump means.

7. A system as set forth in claim 1 including means to cool saidcombustion chamber walls with a flow of cooling water and then injectthe resulting heated water into heat transfer contact with passages ofthe exchanger. i

8. A system as set forth in claim 1 including means to sense thetemperature of the product gas leaving the heat exchanger passages,means responsive to said gas temperature sensing means to causecryogenic liquid to bypass exchanger passages and be admitted to the gasflow leaving the exchanger'for further regulating'the temperature ofsaid product gas.

9. A system as set forth in claim 1 wherein the water injecting meanscomprises a plurality of nozzles angularly arranged in an annular arrayto direct a fogging spray in a generally conical pattern into the hotcombustion gases.

10. A system as set forth in claim 1 wherein the fuel burner and airblower combination are removably connected as a unit to one end of thecombustion chamber and wherein the water injecting means is located atthe heat exchanger end of the combustion chamber.

11. A system as set forth in claim 4 wherein at least four tube bundlesare vertically stacked and conduit means connects pairs of said bundlesto create parallel flow of the liquid in said pairs.

12. A system as set forth in claim 4 including a guidance elbowconnecting said combustion chamber and said vertical stack, baffle meansin said elbow to direct the heat transfer mixtureuniformly from ahorizontal flow to a vertical flow.

13. A system as set forth in claim 4 wherein the combustion chamber isan elongated cylinder and saddle means support the cylinder to permitfree longitudinal movement thereof caused by expansion and contractionresulting from temperature change.

14. A system as set forth in claim 6 including means to adjust thetemperature of the water in the sump means.

15. A system as set forth in claim 1 wherein the fuel burner comprisesan annular manifold means, a plurality of injection tubes extendingradially inwardly from said manifold means, a plurality of ports in eachof said tubes to permit the exhaust of fuel therefrom, means to supplythe manifold means with fuel, said air blower positioned upstream ofsaid burner to direct a flow of air across said tubes, and said mixturetemperature responsive means controlling the fuel supply to the manifoldmeans and the air supply to the air blower.

16. A heat transfer system for heating a fluid comprising a fuelcombustion unit for producing large volumes of hot combustion gases, anelongated tunnel through which the gases are directed for completingcombustion thereof, means at the discharge end of the tunnel forinjecting water spray into the hot combustion gases for producing agas-steam heat transfer mixture, a heat exchanger tower having aplurality of tube bundles through which the fluid is circulated forheating, means for directing the gas-steam mixture from the tunnel insubstantially uniform cross-sectional flow into the tower and into heatexchange contact with the tube bundles for heating the fluid.

17. A method of vaporizing a cryogenic liquid comprising, producinglarge volumes of hot combustion gases, reducing the temperature of thehot combustion gases by contacting said gases with a fogging spray ofwater whereby a substantial portion of the water spray is vaporized andthe temperature of the resulting combustion gas-steam mixture is reducedto within the range of from about l2Q-350 F, directing said gassteammixture to a heat exchanger containing a plurality of tube coilsarranged in a vertical array, maintaining a flow of cryogenic liquid tosaid coils, passing said gas-steam mixture upward through said coils toheat the cryogenic liquid therein, and controlling the temperature ofthe cryogenic vapor leaving the coils according to the temperature ofthe mixture leaving the exchanger.

18. A method as defined in claim 17 including sensing the exhausttemperature of the mixture exiting the heat exchanger and controllingthe production of the hot combustion gases in response thereto tomaintain the exhaust temperature within the range of from about 1 10-l70F.

19. A method as defined in claim 17 including regulating the temperatureof the vaporized cryogen exhaust leaving the exchanger by introducingcryogenic liquid into the exhaust in amounts necessary to main tain adesired temperature level.

20. A method as defined in claim 18 including producing said hotcombustion gases by burning a fuel in the presence of oxygen,controlling the amount of fuel and oxygen supplied so as to fully burnthe fuel and leave substantially no uncombined oxygen.

21. A method as defined in claim 17 wherein the temperature of thegas-steam mixture is reduced to about l50-l90 F.

22. A method as defined in claim 18 wherein the said exhaust temperatureis maintained within the range of from about l30-l40 F.

1. A heat transfer system for vaporizing cryogenic liquid to a productgas comprising, a fuel burner and air blower combination for producinglarge volumes of hot combustion gases, a combustion chamber into whichthe combustion gases are directed for completing combustion thereof,means for injecting water spray into the gases after substantiallycomplete combustion for vaporizing the water and producing a gas-steamheat transfer mixture, a heat exchanger through which the gas-steammixture from the combustion chamber is directed having passages forcirculation of the cryogenic liquid, the heat transfer mixture being indirect heat exchange contact with the cryogenic passages for vaporiZingthe liquid to a product gas, means for sensing the temperature of theheat transfer mixture leaving the exchanger, and means responsive to thetemperature sensing means for controlling the firing rate of theburner-blower combination to regulate the temperature of the product gasleaving the exchanger passages.
 2. A heat transfer system as set forthin claim 1 wherein the combustion chamber comprises an elongatedcylinder of double-walled construction to form an annular coolingpassage around the chamber, the outer of said walls having portsproviding for the admission and exhaust of passage cooling water.
 3. Aheat transfer system as set forth in claim 2 further including helicalbaffle means between the walls of said cylinder to channel the coolingwater flow in a helical pattern.
 4. A heat transfer system as set forthin claim 1 wherein the heat exchanger comprises a plurality of tubebundles arranged in a vertical stacked array, said combustion chamberdirecting said heat transfer mixture into the lower of said tube bundleswhereby the mixture passes up through the vertical array.
 5. A heattransfer system as set forth in claim 4 including means to direct thecryogenic fluid flow through said tube bundles in co-current flowrelationship with respect to the heat transfer mixture.
 6. A heattransfer system as set forth in claim 4 including sump means to collectliquid condensed on said tube bundles for reuse, and further means totrap water leaving the heat exchanger and return the same to the sumpmeans.
 7. A system as set forth in claim 1 including means to cool saidcombustion chamber walls with a flow of cooling water and then injectthe resulting heated water into heat transfer contact with passages ofthe exchanger.
 8. A system as set forth in claim 1 including means tosense the temperature of the product gas leaving the heat exchangerpassages, means responsive to said gas temperature sensing means tocause cryogenic liquid to bypass exchanger passages and be admitted tothe gas flow leaving the exchanger for further regulating thetemperature of said product gas.
 9. A system as set forth in claim 1wherein the water injecting means comprises a plurality of nozzlesangularly arranged in an annular array to direct a fogging spray in agenerally conical pattern into the hot combustion gases.
 10. A system asset forth in claim 1 wherein the fuel burner and air blower combinationare removably connected as a unit to one end of the combustion chamberand wherein the water injecting means is located at the heat exchangerend of the combustion chamber.
 11. A system as set forth in claim 4wherein at least four tube bundles are vertically stacked and conduitmeans connects pairs of said bundles to create parallel flow of theliquid in said pairs.
 12. A system as set forth in claim 4 including a90* guidance elbow connecting said combustion chamber and said verticalstack, baffle means in said elbow to direct the heat transfer mixtureuniformly from a horizontal flow to a vertical flow.
 13. A system as setforth in claim 4 wherein the combustion chamber is an elongated cylinderand saddle means support the cylinder to permit free longitudinalmovement thereof caused by expansion and contraction resulting fromtemperature change.
 14. A system as set forth in claim 6 including meansto adjust the temperature of the water in the sump means.
 15. A systemas set forth in claim 1 wherein the fuel burner comprises an annularmanifold means, a plurality of injection tubes extending radiallyinwardly from said manifold means, a plurality of ports in each of saidtubes to permit the exhaust of fuel therefrom, means to supply themanifold means with fuel, said air blower positioned upstream of saidburner to direct a flow of air across said tubes, and said mixturetemperature responsive means controlling the fuel supply to the manifoldmeans and the air supply to the air blower.
 16. A heat transfer systemfor heating a fluid compriSing a fuel combustion unit for producinglarge volumes of hot combustion gases, an elongated tunnel through whichthe gases are directed for completing combustion thereof, means at thedischarge end of the tunnel for injecting water spray into the hotcombustion gases for producing a gas-steam heat transfer mixture, a heatexchanger tower having a plurality of tube bundles through which thefluid is circulated for heating, means for directing the gas-steammixture from the tunnel in substantially uniform cross-sectional flowinto the tower and into heat exchange contact with the tube bundles forheating the fluid.
 17. A method of vaporizing a cryogenic liquidcomprising, producing large volumes of hot combustion gases, reducingthe temperature of the hot combustion gases by contacting said gaseswith a fogging spray of water whereby a substantial portion of the waterspray is vaporized and the temperature of the resulting combustiongas-steam mixture is reduced to within the range of from about 120*-350*F, directing said gas-steam mixture to a heat exchanger containing aplurality of tube coils arranged in a vertical array, maintaining a flowof cryogenic liquid to said coils, passing said gas-steam mixture upwardthrough said coils to heat the cryogenic liquid therein, and controllingthe temperature of the cryogenic vapor leaving the coils according tothe temperature of the mixture leaving the exchanger.
 18. A method asdefined in claim 17 including sensing the exhaust temperature of themixture exiting the heat exchanger and controlling the production of thehot combustion gases in response thereto to maintain the exhausttemperature within the range of from about 110*-170* F.
 19. A method asdefined in claim 17 including regulating the temperature of thevaporized cryogen exhaust leaving the exchanger by introducing cryogenicliquid into the exhaust in amounts necessary to maintain a desiredtemperature level.
 20. A method as defined in claim 18 includingproducing said hot combustion gases by burning a fuel in the presence ofoxygen, controlling the amount of fuel and oxygen supplied so as tofully burn the fuel and leave substantially no uncombined oxygen.
 21. Amethod as defined in claim 17 wherein the temperature of the gas-steammixture is reduced to about 150*-190* F.
 22. A method as defined inclaim 18 wherein the said exhaust temperature is maintained within therange of from about 130*-140* F.